digital led vu meter

Using the LM3915 to drive a digital LED VU meter

I choose this particular circut after long debate for the following reasons:

1. simple low component. easy circut board to etch.

2. part availability and cost effectiveness,  this stuff is cheap-cheap

3. the ability to daisy chain the chips with pin 9 to add additional sets of 10 LEDs; with one chip I can make 10 LEDs  add two more chips and I can have 30 LEDs per side.

4.  to make a conventionl 30 LED Stereo VU (60 LEDs)  is  not cost effective at all. Kits I have found,  not even close as simple.  way over priced.  But they will take the super brights.

Is there a chip that can do the same as LM3915 but put out a 3.5v that will drive my super brights? (3.5 3.8v max)

or could i just modiy each pin out; put an op amp on it and still keep the end function the way I want it. (sweet and simple and super bright)

Or is this an impossible dream?  And am I dreaming now?  pinch-pinch--punch......nope, I'm awake.

myonus

Be not guided by morality, but rather, integrity.

The LM3915 will operate from 3V to 25V, but being open collector (GND switching) you only need supply the LED +ve voltage to the LEDs using the same GND as the LM3915 (eg, vehicle +12V to the LM3915 and an LM317 tuned to 3.5V for the LEDs. R1 = 120R and R2 = 220R = 3.54V output). The LM3915 outputs will handle (sink) currents up to 30mA. (A 1.5A LM317T will handle a max of 50 30mA LEDs if bar-mode used, but it will current limit if needed.) I presume you are using additional circuitry for the conversion from linear voltage to VU?

Im not sure,  I suppose I would have to,  but the book im reading that was talking about it only explains the circuts diagrams.  Im just trying to decypher the authors intentions.

30 LEDs in mono configuration VU meter

Written in 2000,  anything isd possible.  This is what I came up with.  I know one thing for sure.  This would look really cool sewn into the fabric of my rear seats somehow.

Be not guided by morality, but rather, integrity.

LM3914 is linear, 3915 logarithmic, 3916 VU. What is the range of the display you are looking for? The 3915 will do 30db. Cascading for multiple 30 db ranges requires circuitry changes. Info from NS databook circa 1982.

Thanks Ween. I was thinking of the 3914.

Thanks everyone for the heads up on this curious circut.  Went to TI site and did a quick review of these new update march 2013 datasheets.  Looks like there is quite a bit thats changed since the publication that I'm reading.

There are several points i will still need to consider,  and confirmation that yes these can be cascaded together for an increased resolution of the dot display or bar display depending on how you wire pin 9.

Different additional circuts will be required for the 3916 to operate in true VU which has different scale divisions than the normal linear mode that Im used to.  I think in this specific install; since its really not measureing but a peak indicator of the pre-amp,  I will be just as satisfied with the less complicated linear version. 

The datasheets do indicate that multiple chips can be cascaded, and a small circut can be added to increase the DB.

Scale anywhere from 1.2V to 12V independent of supply voltage. LED brightness is easily controlled with a single pot.

and finally confirmed,  yet absolutely no examples of a 3 chip cascaded system in bar graph display mode.  giving a total of 30 LEDs on a mono setting. Which is exactly what i want.

However i am still not convinced that this is as simple as that, as i found some older material saying that when cascading 2 chips, here ya go,  example 1-4.  when cascading 20 LEDs or more,  its so unclear,  obviously the directions:

Capacitor C1 is required if leads to the LED supply are 6< lang=JA size=1>< lang=JA face="Arial" size=1>″ or longer.

For bar mode, connect pin 9 to pin 3. VLED must be kept below 7V or dropping resistor should be used to limit IC power dissipation.

Here is where I get lost:

20 or More LEDs: Connect pin 9 of the first drivers in the series (i.e., the one with the lowest input voltage comparison points) to pin 1 of the next higher LM3916 driver.

Continue connecting pin 9 of lower input drivers to pin 1 of higher input drivers for 30 or more LED displays.

The last LM3916 driver in the chain will have pin 9 left open.

All previous drivers should have a 20k resistor in parallel with LED #9 (pin 11 to VLED).

I cant get past the bold areas.  what I'm missing is the example.  thats ok, let me try this

 

 

higherst chip 3     >>[chip 3 - pin 9] left open

next higher chip 2    >>[chip 2 - pin 9] to [chip 3 -  pin 1]

lowest chip 1   >> [chip 1 - pin 9] to [chip 2 - pin 1]

Make a virtual LED out of  LED # 10 by adding a resistor 20k from pin 9 to 10 and 11 to 10  - that way LED #10 is a smooth transition to the next chip.

Do the same with LED 19 20 and 21

**************oooooooooo*************

Is that what im suppose to do??  or have i been reading too much science fiction,  And have certainly not pervected the flux capacitor.

OK everybody at once.......  do I geta woot woot?!?!?  

        or a Boot Boot?!?!? 

 

I really hope that somthing out of this was useful. 

One thing for sure:  Knowledge is power,  and power is in the puddin'

----MYONUS

Be not guided by morality, but rather, integrity.

Use LM3915s with one LM3916. Last night I googled lm3916 cascading & lm3916 cascading three 3 and found refs such as allaboutcircuits...t-60335. It also mentions being wary of the chip dissipation when used in bar mode (use a heatsink if required). I was going to reply that you can't use a pot to vary the brightness in bar mode, but you can. I didn't realise that pot is used to control the current limit of (each) output. (Funny - I wonder if I knew that "back then". I used an LM2917 with 2 linear LM3914s in a (round) electronic speedo (or tachometer) with a digital center display back in the late 1970s (yep, horses drew fast carts back then). I can't recall a dimmer control which of course would have been essential, though I probably would have used a PWM to dim the digital LED segments as well. Maybe I'll check - I found the PCB drawing a while ago, tho not its circuit. Ah, yet another unfinished (35 year old) project. But these days you can buy them. Back then it was fiction, though not as real as other "impossible" things I used to do... and still seem to do!)

great find,  and three was all i was interested in.

And by the way have you read the march updated datasheets for these lil fellas?  its a good read/ refresher.  And I agree 1 3916 and 1 3915 and a 3914 and im gonna gonna rock it like a hurricane!  yeaaaaaa!

So did I get a woo hoo,  or a booo hooo??????????

Thanks again,  like always you simplified my week.  You should get a pay pal account so the appreciatve could buy ya a Fosters for all your hard yakka,

Hoo Roo Ta,  Spark

-myonus

Be not guided by morality, but rather, integrity.

LOL - considering my income hassles, maybe I should go pro. But that's not why I do it... Fosters - I wonder if we even make that anymore. I recall buying some Fozzies in London to take back to some people I was staying with in the walled city of Berlin. YUK! I presume the pommie brewing water disagreed with its yeast. A few years later I was educated by some country boys as to how bad Fosters was. They got me onto Melbourne & Victoria Bitter - the latter became the norm for drinkers a decade or 2 ago. Alas by then I was already onto others - generally small independent brewers which had great beers. In fact I learned that brewers I fell in love with (Cascade, Hahn etc) would last a year or 2 before being bought by the big multinational brewers, though Boags has lasted and is still uncorrupted. Not that beer is my drink of choice - I usually sink ciders, or gins, or vodkas, or.... Oh dear, I digressed. (I'd hate to see some mod delete this reply as well.) Back to the LMs. Yeah - instead of recovering my old (lost) data I downloaded a few new datasheets. I may compare to my ~1978 National Linear Data Book (maybe the current control is a newer addition, or maybe I missed that entirely though it's more likely I have simply totally forgotten!). Incidentally, that Linear and another CMOS (Logic) databook is what gave me my electronics education. I'd stare at the strange specs & timing diagrams etc and eventually they started to make sense. I'd then figure ways of combining the various building blocks (chips or circuits) to achieve things. One of the first was an electronic Halda - an accurate odometer with 10m or 10yd resolution for car rallies. After I built it I found it was apparently impossible according to 3 electronics enthusiasts two of whom were engineers. They argued you could not do the frequency multiplication that was required. (PLLs - Phase Locked Loops - were uncommon back then - not that they were suited to the range of a speedo.) I guess it was a pity that mine worked fine, and much cheaper than the eventual electronic Halda that came out years later for ~$400 (circa 1980). That was one of three "impossible" I did at that time... Those chips revolutionised electronics. No longer were precision or mass transistor designs needed - just chips with interfacing. And despite PICs & uPCs, many still survive - eg, voltage regulators (especially the LM317), the 555 timer, the 4017 one-of-ten decade counter (eg, SAAB headlight dipper relays), countless Op-Amps, etc. Some have been put to novel uses (eg, the 4017) though often I think some are inappropriate - eg, I have seen countless 555 circuits to monitor inputs for solar or battery powered stuff and the 555 takes 10mA; simple transistor or FET circuits would consume uA - even small PICc etc only consume nA - well under uA (1uA being 1/10,000th of what the 555 consumes).

this book im reading is full od 391x.  I gonna replace mt dash on my car with a digital one  described n it.  maybe even modify some stuff too.I just finished etching the board for my coltage regulator for my bench 12v test power supply.  I sure do love this new etchant this guy makes for me in California.  Its a salt crystal you mix with water 4 to 1.  Anf its higghly caustic for about 30 minutes,  then it turns blue and its harmless.

Anf the best thing is a can make enough with 1.5 oz of water and 1/2 oz of salts. and etch the whole side of my little power regulator.  If you want to try it,  I'll send you a sample bottle.  Next time I order.  Fantastic stuff. Not tank or exaust required,  Just a plasticc ware dish, and a natural fiber painters brush. and some rubber gloves.  now i can hook up my new pcb drill and get back busy on the power distibution for the car install.  yep the same one,  still have been pluggin away at it for weeks now,  every day.  Im making and fabricating almost everything from scratch. 

And its been alot of fun,

Im gonna finish my Shiner Bock from good ol Shiner Texas, and hit the headboard- gnite

-myonus

Be not guided by morality, but rather, integrity.